The present invention relates to liquid heat exchangers and, in particular, to an internally mounted, probe-type exchanger, which mounts to a single access port of a storage tank, such as a conventional, domestic water heater, and through which a low pressure heated liquid is distributed from a boiler.
Renewable fuel heating systems have become increasingly more popular as fossil fuel costs have risen over the years. Wood fired boilers such as manufactured by the present assignee, Central Boiler, Inc. of Greenbush, Minn. have found particular consumer acceptance. These boilers provide a free-standing housing, which encases an insulated liquid heat exchanger, and which surrounds a wood fueled firebox. Heated liquid is conducted at low pressures underground from the boiler through plastic conduits to interior conduits at the heated premises. Liquid-to-air heat exchangers are provided about the residential or industrial premises to transfer the heat to the interior space.
For many systems, the heated liquid may also be conducted to a separate, liquid-to-liquid heat exchanger at a water heater provided at the premises. Many such exchangers provide an externally mounted assembly which couples to top and bottom ports of a provided hot water heater to obtain a closed loop, thermo-siphon flow at the water heater.
Although thermo-siphon assemblies have been used for many years, they present a variety of deficiencies. While conceptually relatively simple, such assemblies frequently require professional installation. Proper alignment must also be maintained to prevent airlock. Alternatively, periodic purges must be performed, either manually or via an automatic purge valve. Scale within the boiler supply loop can also collect at flow transition regions within the system to restrict flow and reduce efficiency. Most significantly, the external mounting of such assemblies frequently requires that the exchanger be separately insulated to reduce radiant heat to the living space from the exchanger, which can create uncomfortable ambient temperatures during warm weather conditions.
Other, multi-ported, internal assemblies are also known. One, in particular, provides a specially constructed liquid storage container which includes an integrated, serpentine flow column. Separate inlet and outlet ports at the tank walls direct the heated liquid to the ends of the heat exchanger.
In appreciation of the foregoing deficiencies, the present invention provides an internally mounted liquid-to-liquid heat exchanger which can be secured without modification to the sacrificial anode port or bunghole provided with conventional domestic water heaters. A threaded manifold fastener seals the exchanger assembly within the tank cavity. Exposed inlet and outlet ports direct supply and return flow to the boiler. Installation can be performed by non-professional installers in a matter of minutes. Radiant heat transferred to the ambient environment is also substantially reduced.